Archives

Application – Standard Models

Breaker Failure

BE1-BPR relays are intended to provide a preprogrammed solution for most

breaker failure relaying applications. Breaker failure relaying is the use of a

current monitoring relay to determine whether or not current continues to

flow into a faulted circuit after a breaker has been instructed to interrupt the

circuit. If current continues to flow into the faulted circuit after a defined

period of time has elapsed (sufficient for the breaker to have interrupted the

current), the circuit breaker is considered to have failed. Steps must then be

taken to trip the next set of breakers in the power system to prevent system

damage. Breaker failure schemes must be designed to isolate both the faulted

circuit and the failed breaker.

Several reasons why a breaker fails to clear a fault are:

• Trip circuit is open (broken wire, blown fuse, open trip coil).

• Interrupting mechanism stuck, leaving a single phase of a three-phase circuit

connected.

• Interrupter flash-over due to the loss of dielectric strength through

contamination or damage.

• Operating mechanism failed to operate.

Breaker Reclosing

BE1-BPR relays can be configured as multiple shot reclosing relays that operate in

parallel and independently from the breaker failure function.

Three major factors should be considered when establishing a reclosing philosophy.

• Desired number or reclosure attempts.

• Time delay between breaker opening and reclosure.

• Supervisory control.

The first major factor is the desired number of reclosure attempts. Where most

faults are attributable to heavy tree exposure, as in distribution networks, multiple

reclosure attempts are common. This is possible because of low voltage levels and

is desirable considering customer inconvenience during outages. BE1-BPR relays

are programmable for up to three reclosure attempts per sequence. This allows

tailoring of the reclosing sequence to the specific needs of the circuit.

The second major factor is the time delay between breaker opening and reclosure.

On sub-transmission and distribution networks, it is necessary to ensure that motors

are no longer running and that local generation is off-line prior to attempting reclosure.

At the same time, a rapid reclosure minimizes damage, ionization, and system shock

in transmission networks. After the first reclosure attempt, additional attempts are

generally delayed to allow for de-ionization of the interrupter. BE1-BPR relays have

three reclosing shots and each shot has a programmable time delay. 

Three outputs are available. They are CLOSE, RECLOSE FAIL, and LOCKOUT.

A third major factor to be considered in reclosing is supervisory control. Supervisory

control allows the operator to maintain control of the system at all times. BE1-BPR

relays have two supervisory inputs (WAIT and LOCKOUT). WAIT stops the reclose

sequence at any point and allows the sequence to continue when the WAIT input is

removed. LOCKOUT drives the reclose function immediately to lockout status and

takes precedence over all other inputs.

Breaker failure relays detect these conditions and initiate backup procedures.

Breaker failure relays are applied on a per breaker basis. That is, one breaker

failure relay for each breaker in the substation. BE1-BPR relay outputs must be

arranged to initiate the tripping of all the circuit breakers necessary to isolate

the fault if the protected circuit breaker fails to operate. The relay may also

need to initiate transfer tripping of remote breakers to accomplish this task.

Transfer tripping of the remote line end for a breaker failure should also block

reclosing of the remote circuit breakers. External lockout  relays are typically

used to trip and block reclosing of the backup breakers because they normally

require a positive operator action to reset them.

Typically, breaker failure protection is applied to transmission and sub-transmission

systems. However, breaker failure protection may be applied to any portion of the

power system where failure of a circuit breaker to operate properly could result in

severe system damage or instability. Breaker failure protection can also be used to

selectively clear a failed breaker in a station with multiple buses without clearing

the entire station.

BE1-BPR Breaker Protection Relays are three-phase and neutral, 

microprocessor based relays designed to provide power systems 

with protection and security against monitored breaker failure or

to initiate multiple shot breaker reclosings.

These relays incorporate a powerful means of programming internal

relay logic to satisfy a wide range of user requirements without making

any relay hardware changes. Microprocessor-based design provides

the basic features of a programmable logic controller (PLC) combined

with an instantaneous overcurrent module.

Cased in a 19 inch rack-mount or a vertical panel mount, the relay offers

installation versatility. A wide temperature, 2 lines by 16 character display

provides diagnostic and setup information. Two RS-232 serial ports (one

each front and rear) and one RS-485 serial port (rear) provide remote

communication and relay control.

Built-in diagnostics and monitoring features provide information for both

the health of the relay and the health of the breaker being monitored.

Relay diagnostics include continuous background monitoring of the

power supplies, analog-to-digital (A/D) converter, random-access memory

(RAM), read-only memory (ROM), and electrically-erasable programmable

ROM (EEPROM). A dedicated alarm (ALM) relay output provides power 

supply, microprocessor, and software alarm status. Breaker diagnostics

include a timing diagnostic log, breaker contact duty monitoring, breaker

resistor protection, and breaker arc detection.

Other monitoring features include oscillographic fault records and fault

summary logs. BE1-BPR relays use the Inter-Range Instrumentation Group

(IRIG), Format B for high timing accuracy and resolution.